The objective of this research is to investigate the basis of the increased Na-transport accompanying mouse mammary tumorigenesis and whether this increased Na-transport contributes to tumorigenesis. Hormones play an important role in stimulating proliferation, differentiation and tumorigenesis in the mouse mammary system. Hormones have been shown to affect ion transport as part of their stimulation of cellular metabolism in other systems. Ion transport has been shown to play a role in the transport of sugars and amino acids, in the synthesis of protein, RNA and DNA, and in mitogenesis. We have experimental data which demonstrates an increase in Na-transport with mouse mammary tumorigenesis. We propose to investigate the effects of hormones in altering ion transport as part of their stimulation of proliferation and differentiation of mature virgin mammary gland, the role of ion transport in nutrient transport of normal and tumor mammary cells, and the significance of ion transport associated with hormone-dependent tumors. The results of the proposed research will help determine possible hormonal regulation of ion transport (and the role of ion transport in hormone action) and the influence of ion transport accompanying proliferation, differentiation and tumorigenesis of the mouse mammary system.